Regulating Pressure-Volume Control of a Gas Blanketing Liquid R-124

A system for storing and circulating a refrigerant liquid [R- 124 (chloro- tetrafluoroethane)] includes a reservoir and a subsystem that regulates the pressure of nitrogen gas in the head space of the reservoir. The purpose of the pressurization is to prevent cavitation in a pump that circulates the liquid. It is necessary to keep enough nitrogen in the system to keep the pressure high enough to prevent cavitation even when the liquid is at its coldest and thus at its smallest volume. It is also necessary to satisfy a competing requirement to, when the refrigerant is at its warmest and thus at its greatest volume, prevent the pressure from exceeding the level at which a relief valve opens and vents the head-space gaseous mixture of refrigerant vapor and nitrogen to the atmosphere. The pressure-control subsystem includes a supply of nitrogen at a pressure of 80 psig (gauge pressure of 552 kPa), a commercial electronic pressure regulator, a programmable-logic controller, and pressure and temperature sensors in the reservoir. The pressure-control subsystem adjusts the nitrogen pressure to the optimum value for the sensed temperature, thereby preventing both cavitation and venting.